Medical and hospital supplies have been packaged and then sterilized to reduce the hazard of infection in hospitals and clinics. Packages previously employed have suffered from various disadvantages. Some of the packages have been difficult to open, requiring tearing or cutting of the packaging material. Other packages have the disadvantage that they are sealed by means of pressure-sensitive adhesives which permit the package to be opened and then resealed merely by pressing the adhesive-coated surfaces together. The pressure-sensitive seals are such that it cannot be readily determined by visual observation whether the seal has been broken whereby the contents may have been contaminated by air borne bacteria. In other prior known packages, the seal is such that it cannot be determined by simple visual inspection whether the seal is complete and impermeable to bacteria or whether the seal may have been broken in handling prior to use.
More recently sterile packages have been designed whereby the validity of a heat seal can be ascertained visually. Thus, U.S. Pat. No. 3,533,548 discloses a method for determining visually whether or not a certain area of a plastic film or sheet is securely sealed to an adjacent paper backing by coloring the plastic film in a relatively light shade of a selected color and heat sealing the sheets together. The sealed areas appear much darker than unsealed areas and thus a gap or interruption in the seal can be observed visually. Similarly, according to U.S. Pat. No. 4,097,236 a break in the heat seal between a clear plastic member and a paper member can be detected visually by coloring the paper member. If there is a break in the heat seal, the clear plastic member takes on an opaque appearance in the area of the broken seal.
A major drawback of the means for determining failure of the heat seal according to the above-discussed patents resides in the fact that inspection of the seal in many instances will require inverting the packages since the seal is visible only on one side of the package. Such procedure can very well interfere with high speed assembly line production of packages required to today's economy.
The package of the present invention overcomes these objections and drawbacks and comprises broadly a pair of front and rear panels made of nonporous transparent plastic sheet material, e.g. a polyolefin material such as polyethylene, which are sealed together about their peripheral edges to define a recess or pocket for holding the contents. Prior to being heat sealed together one or both of the panels is coated, at least in those areas which are to be heat sealed, with an adhesive, which, after application and drying, is opaque. Upon being subjected to heat and pressure in the seal area, the adhesive becomes transparent, whereby the presence of an integral seal which is impermeable by bacteria is readily determined by mere visual observation from either side of the package. When the heat seal is ruptured, as for example in opening the package, the seal areas on both the front and rear panels become opaque. Thus, this invention provides means for determining whether the seal is incomplete or has been ruptured whereby air borne bacteria may have contaminated the contents.